Attorney General Eric Holder today said he was unable to answer questions about an investigation into an Associated Press story published a year ago that contradicted the White House's claim that officials knew of no attacks planned on U.S. soil for the anniversary of Osama bin Laden's death.

The FBI interviewed Holder in June 2012 as part of its investigation into national security leaks in the Obama administration because of his frequent interaction with the media. Holder said during a news conference today that he recused himself shortly after the start of the investigation to avoid the appearance of a conflict of interest, leaving the U.S. Attorney's Office and the deputy attorney general in charge.

"The deputy attorney general would have been the one who ultimately authorized the subpoena that went to AP," Holder told reporters Tuesday. "I'm not familiar with all that went into the formulation of the subpoena ... but I'm confident that the people who are involved in the investigation -- who I've known for a great many years and I've worked with for a great many years -- followed all of the appropriate Justice Department regulations and did things according to DOJ rules."

The Associated Press received a letter Friday from the Justice Department, informing it that investigators had secretly obtained phone records, both from its reporters' personal phones and from phone lines from the AP's offices.

AP President and Chief Executive Officer Gary Pruitt sent a letter to Holder Monday, saying, "There can be no possible justification for such an overbroad collection of the telephone communications of the Associated Press and its reporters. These records potentially reveal communications with confidential sources across all of the newsgathering activities undertaken by the AP during a two-month period, provide a road map to AP's newsgathering operations, and disclose information about AP's activities and operations that the government has no conceivable right to know."

Deputy Attorney General James Cole responded to that letter today, saying the measures taken were consistent with DOJ policy.

"As you know, for each of the phone numbers referenced in our May 10, 2013, letter there was a basis to believe the numbers were associated with AP personnel involved in the reporting of classified information," Cole wrote in a letter to Pruitt.

He said the department engaged in 550 interviews and looked at "tens of thousands of documents" before obtaining the phone records.

One of the concerns surrounding the investigation is that the administration might have revealed "communications with confidential sources," according to the AP.

At his 2009 confirmation hearing, Holder expressed support for a law to protect the media from being punished for protecting sources.

"I think that the bill that we have strikes a good balance. It's a compromise between the concerns that we had in law enforcement and the intelligence side, and the legitimate interests, I think, of the media," Holder said of the shield proposal that died in the Senate.

Republicans had called for an investigation into Obama-administration leaks, particularly a May 2012 AP story about the CIA's thwarting a terrorist plot originating in Yemen. The Associated Press reported Monday that DoJ officials accessed phone records for reporters involved in that story.

The AP's report Monday drew swift condemnation of the Justice Department for surreptitiously obtaining information on the media.

The American Civil Liberties Union and Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., both expressed concerns that the Justice Department might have overstepped its bounds in obtaining the AP phone records. Republican National Committee Chairman Reince Priebus called on Holder to resign.

According to DoJ guidelines reported by AP, subpoenas for press records must be "as narrowly drawn as possible" and "should be directed at relevant information regarding a limited subject matter and should cover a reasonably limited time period."

The U.S. Attorney's office said, of its investigation into AP, "We take seriously our obligations to follow all applicable laws, federal regulations, and Department of Justice policies when issuing subpoenas for phone records of media organizations. Those regulations require us to make every reasonable effort to obtain information through alternative means before even considering a subpoena for the phone records of a member of the media. We must notify the media organization in advance unless doing so would pose a substantial threat to the integrity of the investigation."

Holder called the information given to the AP, "a very, very serious leak ... among the most serious" he had seen in his 37-year career.

"It put the American people at risk," he said. "That is not hyperbole."